In Malaysia, there is a growing demand for halal pharmaceutical products, especially from conscientious Muslims. For Muslims, seeking halal goods is a must in order to get Allah's blessings. Nevertheless, there are only a few pharmaceutical products in the market with the certified halal logo. Thus, for Muslim consumers in Malaysia, their due diligence effort involves looking at the ingredient listed in the packaging. For many consumers, some of this information is far beyond their common knowledge. If this happens, consumers are actually in the position of having imperfect knowledge. This study was therefore conducted to investigate the factors that caused imperfect knowledge in the buying decisions of Muslim consumers. Questionnaires were distributed to 100 Muslim respondents at public clinics in Putrajaya. This study found that label, awareness, and trustworthy led to imperfect knowledge in the buying decisions of pharmaceutical products among Muslim consumers.